This application pertains to a dual fuel method and system for use with internal combustion engines of vehicles.
As gasoline supplies have decreased and become more costly, the need for alternative fuels and fuel conservation has become greater. Accordingly, alternate sources of fuels and methods of fuel conservation have become more attractive, particularly for internal combustion engines for automotives.
Operation of an internal combustion engine on a liquid fuel and a gaseous fuel increases fuel economy and engine efficiency while at the same time maintaining low levels of undesirable exhaust emissions. Vehicles adapted to operate on either a liquid fuel or a gaseous fuel are sometimes called xe2x80x9cdual fuelxe2x80x9d or xe2x80x9cmulti-fuelxe2x80x9d vehicles.
In order to maximize fuel economy and minimize engine emissions, there has been a trend to use gaseous fuels, such as compressed natural gas (CNG), liquid natural fuels (LNG), such as ethanol, and liquid or liquified petroleum gas (LPG). Gaseous fuels, such as CNG, and LPG, not only provide good fuel economy and low engine emissions, but also provide better cold starting of internal combustion engines.
Gaseous fuels comprise combustible fuels which are gaseous at standard temperature and pressure. Gaseous fuels used by dual fuel vehicles include methane comprising natural gas or compressed natural gas (CNG), hydrogen, etc. The term gaseous fuels also includes liquified petroleum gas (LPG). LPG is particularly desirable as gaseous fuel. LPG under pressure may be either in the gaseous phase, the liquid phase, or both. Examples of LPG are propane, butane, dimethyl ether (DME), etc.
Atmospheric pollution from combustion of hydrocarbon fuels, such as emitted from the exhaust of gasoline fueled automotive internal combustion engines, if not properly controlled, can cause problems. Substantial effort and research has gone into the development of vehicle engines which operate on various lighter hydrocarbon fuels as an alternative to gasoline, such as ethanol, and even those fuels having less complex hydrocarbon molecules with fewer carbon atoms per molecule, i.e., pentane, butane, propane, methane, and even ethane. Natural gas (methane) has been used because of its abundance and clean burning performance, its relatively low costs and its use as a fuel for stationary internal combustion engines. In order to provide an adequate supply in vehicles for fueling vehicle internal combustion engines, the fuel must be stored in highly compressed form, requiring heavy duty, highly pressurized fuel tanks and fuel system components capable of storing gaseous methane at ambient temperatures ranging up to 125xc2x0 F. (51.6xc2x0 C.) and be capable of withstanding high pressures.
Propane on the other hand, can be stored in liquid form and at much lower pressures than methane, e.g. 0 psi at xe2x88x9244xc2x0 F. (xe2x88x9242.2xc2x0 C.), 125 psi at about 70xc2x0 F. (21.1xc2x0 C.) and 260 psi at 125xc2x0 F. (51.6xc2x0 C.). In some geographic locations, supplies of liquid propane fuel for a variety of uses are already relatively abundant and economical.
Various dual fuel systems have been developed utilizing propane as the alternative fuel of choice with pressurized containment and delivery of propane. Typical vehicle propane fuel tank systems commercially available supply propane in gaseous form to the engine intake manifold via a carburetor fuel feed system or an electronic fuel injection (EFI) system.
Many conventional dual fuel systems are expensive and unreliable. Furthermore, conventional dual fuel systems often have two separate systems with many duplicate, redundant and/or extra sets of parts, components, or equipment, such as computers, hoses, burner assemblies, second stage regenerators, etc. Further, conventional dual fuel systems are often bulky and occupy valuable space in the hood (bonnet) of the vehicle. The extra weight of duplicate equipment of conventional dual fuel systems can increase fuel consumption.
Moreover, conventional dual fuel systems often encounter vehicle performance problems at switchover to different fuels. Switchover to different fuels can be unstable due to timing delays of two fuels. For example, when a conventional carbureted dual fuel system is switched from a gasoline mode to a liquified petroleum gas (LPG) mode, gasoline continues to be fed into the engine at the same time as LPG until the gasoline in the float bowl of the carburetor is empty. This can cause flooding and stalling of the internal combustion engine. When a conventional carbureted dual fuel system is switched from an LPG mode to a gasoline mode, the LPG is shut off, but no gasoline will be fed into the engine until the gasoline fills the float bowl of the carburetor. This can cause choking or sputtering of the internal combustion engine.
Conventional dual fuel system with electronic fuel injectors (EFI) encounter similar problems. For example, when a conventional EFI dual fuel system is switched from a gasoline mode to an LPG mode, gasoline continues to be fed to the engine at the same time as LPG until the residual gasoline in the fuel rail and hoses are depleted. This can cause an undesirable mixture of gasoline and LPG which can cause malfunction and/or engine performance problems. Moreover, when a conventional EFI dual fuel system is switched from a LPG mode to a gasoline mode, residual LPG in the fuel rail and hose will continue to flow into the engine with gasoline which can create unstable, rough and uneven vehicle performance.
It is, therefore, desirable to provide an improved dual fuel method and system, which overcomes most, if not all, of the preceding problems.
An improved dual fuel method and system is disclosed which provides a smooth transition from a first fuel to a second fuel. The first fuel can be a liquid fuel, such as gasoline or petro, and the second fuel can be a gaseous fuel, such as liquified petroleum (LPG). The dual fuel system can also be constructed to eliminate costly control elements and duplicate sets of equipment for the LPG system, such as computers, hoses, burners assemblies, second stage regenerators, etc. Advantageously, the improved dual fuel method and system is economical, easy-to-use, and convenient. Desirably, the user-friendly dual fuel method and system is reliable, safe, efficient, and effective. Significantly, the inventive dual fuel method and system provides for better fuel economy, occupies less space, and uses less fuel than conventional bulky dual fuel methods and systems.
The preferred liquid fuel is gasoline, although other types of liquid fuels can be used in some circumstances, if desired. The preferred LPG is propane, although other types of LPG can be used if desired, such as butane, dimethyl ether (DME), etc. The preferred gaseous fuel is LPG, although other types of gaseous fuels can be used in some circumstances, such as compressed natural gas (CNG), etc.
The improved dual fuel method and system is especially useful in a vehicle, such as: an automobile, a taxicab, a sport utility vehicle (SUV), a van, a station wagon, a truck, a motorcycle, a snow mobile, a jet ski, an all terrain vehicle, a ship, an airplane, a tractor, a backhoe, a bulldozer, a crane, or road grading equipment. The improved dual fuel method and system can also be used in other mobile engines as well as stationary engines, such as in power plants, generating systems, etc.
The special method for operating a dual fuel system in accordance with principles of the present invention, comprises the steps of: pumping a first fuel, such as gasoline, to a fuel feeding device; feeding the first fuel (e.g., gasoline) from the fuel feeding device to an engine; and operating the engine with the first fuel in a first fuel mode. When it is desired to change the mode of operation of the engine to operate on a second fuel, such as liquid petroleum gas (LPG), the flow of the first fuel (e.g., gasoline) to the fuel feeding device is stopped. In order to prevent flooding, stalling and malfunction of the internal combustion engine, it is best to wait until the first fuel (e.g., gasoline) is substantially empty from the fuel feeding device so as to prevent the flow of the first fuel (e.g., gasoline) from the fuel feeding device to the engine before opening the second fuel valve (e.g., LPG valve) for feeding, supply and access to the second fuel, e.g. LPG. When the second fuel valve is open, the second fuel (e.g., LPG) is passed to the engine so that the engine can operate on the second fuel in the second fuel mode.
When it is desirable to change the mode of operation of the engine from a second fuel mode to a first fuel mode, the first fuel (e.g., gasoline) is pumped to the fuel feeding device. In order to prevent choking, sputtering, unstable, rough, and uneven vehicle performance, it is best to wait until the first fuel (e.g., gasoline) substantially fills the fuel feeding device before closing the second fuel valve. When the second fuel valve is closed, the flow and feeding of the second fuel to the engine is stopped. Thereafter, the first fuel (e.g., gasoline) is fed from the fuel feeding device to the engine so that the engine can operate on the first fuel.
In one form, the fuel feeding device comprises a carburetor with a float bowl. The first fuel (e.g., gasoline) can be pumped by a fuel pump which operatively associated with the engine.
In another form, the fuel feeding device comprises one or more electronic fuel injectors (EFI) with one or more fuel rails and fuel line(s). The first fuel (e.g., gasoline) can be pumped by a fuel pump which operatively associated with a first fuel tank.
In a preferred form, exhaust gases are emitted from the engine and the oxygen content of the exhaust gases are monitored. A signal, such as an oxygen (O2) signal and preferably a filtered signal, e.g., a filtered O2 signal, is generated based upon a monitored oxygen content of the exhaust gases over a finite selected period of time. The filtered signal can be generated in or associated with an engine control unit (ECU), which controls operation of the valves, such as the second fuel valve (e.g., LPG valve), based upon the filtered signal. Preferably, the second fuel valve is opened when the filtered signal decreases upon changing to the second fuel mode. Also, preferably, the second fuel valve is closed when the filtered signal increases upon changing to the first fuel mode.
In order to increase the reliability and further enhance the failsafe operation of the dual fuel method and system, the filtered signal can be timed to generate a timing signal which provides a timer, sometimes referred to as a xe2x80x9cwatch dogxe2x80x9d timer. In the second fuel mode (e.g., LPG mode), the second fuel valve can be opened upon receiving a timing signal from the watch dog timer if the filtered signal does not substantially change for a preselected (predetermined) period of time. In the first fuel mode (e.g., gasoline mode), the second fuel valve can be closed upon receiving a timing signal from the watch dog timer if the filtered signal does not substantially change for a preselected (predetermined) period of time.
A dual fuel system for a vehicle can also be constructed in accordance with principals of the present invention with a dual fuel engine, such as to drive a vehicle. The dual fuel engine can be powered by separate fuels including a first fuel comprising a liquid fuel, such as gasoline, and a second fuel comprising a gaseous fuel, such as liquified petroleum gas (LPG) or compressed natural gas (CNG). Desirably, the engine is operable and switchable from a first fuel (e.g., gasoline) mode and in a second fuel mode (e.g., gaseous fuel).
A dual fuel system can have an intake manifold which is connected to the engine to pass fuel to the engine. A carburetor can be provided with a float bowl and a valve, such as a butterfly valve, which communicates with the intake manifold to feed gasoline (the first fuel) to the engine when the engine is operating in the gasoline (first fuel) mode. The dual fuel system can also include an air filter which is positioned in proximity to the carburetor. A gasoline tank is preferably provided to store and contain gasoline. A fuel pump can be operatively associated with the engine to pump gasoline from the gasoline tank to the carburetor when the engine is operating in the gasoline mode. A gasoline valve can be provided to control the flow of gasoline to the carburetor. Desirably, a control valve (air valve) is provided which communicates with the air filter and the intake manifold, to pass filtered air from the filter to the gasoline flowing into the intake manifold at an air-fuel ratio regulated by the butterfly valve of the carburetor and/or ECU. Advantageously, a one-way valve is provided to permit the passage of filtered air from the air filter to the control valve (air valve) as well as to prevent the flow of the second fuel to the air filter.
The dual fuel system preferably also comprises a second fuel tank to store and contain a second fuel, such as LPG or CNG. A second fuel valve can be provided to control the flow of the second fuel (LPG or CNG) from the second fuel tank to the control valve. The control valve is operable to pass the second fuel to the intake manifold when the engine is operating in the second fuel mode. The control valve can comprise a dual air valve and a pulse width modulation (PWM) valve. Desirably, an engine control unit (ECU) is operatively associated with the engine, as well as with the control valve, gasoline valve, and second fuel valve, to control the performance of the engine, control valve, gasoline valve, and second fuel valve. A mode selection switch which is operatively connected to the ECU can also be provided to permit the operator or driver to select when the engine is operating in the gasoline mode or in the second fuel mode.
In one form, the second fuel comprises liquified petroleum gas (LPG) and the second fuel valve comprises an LPG valve. The system can include a regulator and a vaporizer connected to the LPG valve to regulate and vaporize the LPG when the engine is operating in the second fuel mode.
In another form, the second fuel comprises compressed natural gas (CNG) and the second fuel tank comprises a CNG tank.
In the preferred form, an exhaust pipe is provided which communicates with the engine to discharge exhaust gases. Desirably, a catalytic converter is provided to minimize emissions of pollutants into the atmosphere from the exhaust gases. Advantageously, an oxygen (O2) sensor is provided which communicates with the engine control unit (ECU) to sense and monitor the oxygen content in the exhaust gases.
A more detailed explanation of the invention is provided in the following detailed description and appended claims taken in conjunction with the accompanying drawings.